Lots of sound feedback here. One thought that I would share in response to Jewbacca's important point regarding adjusting your goals (presumably to be more conservative) in response to how your body feels in workouts is that you can probably throw that idea out when it comes to marathon paced efforts. I have gone through three marathon cycles and 9 efforts at longer marathon paced runs, with that pace being established by recent goal races. Of the 9, I felt relatively good on 3 of them, and even in those 3, at the time I was running them, it seemed like there was no way I would be able to handle that pace for twice the distance. I think that is probably the case for most people trying to run under 2:40 or so. So I would not adjust my marathon goal pace to a slower time based on how I feel during one of those efforts.